LeetCode110. Balanced Binary Tree（平衡二叉树）

110. Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7
Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4
Return false.

---

题目：判断是否是平衡二叉树。

思路：https://leetcode.com/problems/balanced-binary-tree/discuss/35691/The-bottom-up-O(N)-solution-would-be-better.左右子树的高度差不能超过1。

工程代码下载

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        return getDepth(root) != -1;
    }
private:
    int getDepth(TreeNode* root){
        if(root == nullptr)
            return 0;
        int left = getDepth(root->left);
        if(left == -1) return -1;
        int right = getDepth(root->right);
        if(right == -1) return -1;

        if(abs(right-left) > 1)
            return -1;
        return 1 + max(right, left);
    }
};